<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>

    <script src="./js/jQuery/jquery-1.12.4.min.js"></script>

    <script>
        $(function(){
            // 获取到标签对象
            var $mybtn = $("div");
            // 进行样式修改
            $mybtn.css({"height":"100px"});
            // has方法
            $mybtn.has("#btn").css({background});
        })

    </script>

</head>
<body>
<div>
    <input type="button" value="itcast" id="btn">
</div>

<div>
    <input type="button" value="heima" class="btn">
</div>
</body>
</html>